Device and method to bend the rolls in a rolling stand

ABSTRACT

A device to bend the rolls ( 10 ) in a rolling stand, wherein each roll to be bent ( 11 ) is rotatably mounted in two corresponding chocks ( 12 ) each associated to two series of two double-effect actuators ( 13 ), for a total of four actuators ( 13 ) for each chock. Each actuator ( 13 ) is disposed on opposite sides of the corresponding chock ( 12 ) with respect to the axis of rotation (Y) of the roll ( 11 ) to be bent.

FIELD OF THE INVENTION

[0001] The invention concerns a device and a method to achieve bendingof the rolls, both positive (in) and negative (out), in a rolling stand,advantageously of the working rolls.

BACKGROUND OF THE INVENTION

[0002] In a conventional rolling stand, for example in a four-high orsix-high stand with both positive and negative bending of the workingrolls WR, the bending force is generally managed, for each chock, bymeans of four, six or eight actuators or hydraulic jacks A (FIG. 1a).

[0003] The actuators A are single effect and therefore two (or four) ofthem thrust the upper chock GWR upwards (positive bending), while two(or four) of them thrust the same upper chock GWR downwards (negativebending).

[0004] Normally, considering the forces in play required to perform aneffective “mechanical” rounding of the working rolls, the piston of eachactuator is rather bulky, so that this solution is limited with regardto the maximum bending force applicable to the working roll. Moreover,this conventional solution requires that seatings be made (in thehousing or in blocks connected to the housing) above and below the finsD of the chocks GWR of the working rolls WR. The bulk may be such thatthe solution with both positive and negative bending becomes difficult,especially in stands where the working rolls WR must also be displacedaxially (shifting).

[0005] Very often, considering the limits of space, it is necessary tomanage without applying negative bending, thus considerably reducing (byabout a half) the capacity to dynamically control the strip profilewhich can be obtained with both positive and negative bending.

[0006] The presence of play and friction usually causes anindetermination in the passage from negative bending to positive bendingand vice versa, unless particular strategies are adopted such as the onewe shall now illustrate.

[0007] With reference to the diagram in FIG. 2, which refers to aconventional embodiment, for example that shown in FIG. 1a, where thex-axis shows the desired total bending force (FTD) and the y-axis showsthe actual total bending force (FTE), if the total bending has to benegative, pressure is applied to the negative bending hydraulic jacksand the positive bending hydraulic jacks are kept on zero. If the totalbending is to be positive, a symmetrically opposite approach is used.

[0008] As we have seen, however, due to the play and friction, amanagement of this type creates an area of indetermination AI, or greyarea, around the zero.

[0009] In other words, it is impossible to be sure of the real value ofthe actual total bending force (FTE) in the shaded area AI in FIG. 2,with respect to the desired bending force (FTD).

[0010] In a conventional embodiment, for example that shown in FIG. 1a,to eliminate the problem illustrated above and to obtain a substantiallylinear resulting force F (FIG. 3), it is possible to manage the forcesas follows.

[0011] When the total bending is positive, the negative bendinghydraulic jacks generate a constant negative force, while simmetricallythe opposite happens when the total bending is negative.

[0012] The state of the art comprises document JP-A-62009708, whichdiscloses a roll bending device wherein, for each roll chock, aplurality of double-effect actuators are interposed between an upper finand a lower fin of the chock. When the working rolls are rearranged, alower reinforcing roll is moved down and an upper reinforcing roll ismoved up by a balance cylinder. By means of two actuators, the chock ofthe upper working roll is moved up and the chock of the lower workingroll is moved down to the lowermost position. By that operation, a firstlateral wheel of the chock of the lower working roll is ridden on arearranging rail, so that the same chock is able to be pulled out. Onthe other hand, the upper fin of the chock of the upper roll issupported by the piston rod of the corresponding actuator and a firstgap is generated between the arm and the piston rod of the otheractuator. A second gap is generated between a second wheel set on theupper fin of the chock of the upper working roll and a rearranging rail.This device, even if it uses double-effect actuators, is verycomplicated and cumbersome and does not provide for the control of smallforces to obtain bending around the zero position.

[0013] The present Applicant has devised the device according to theinvention to overcome these shortcomings.

SUMMARY OF THE INVENTION

[0014] The device and method to bend rolls in a rolling stand accordingto the invention are set forth and characterized in the respective mainclaims, while the dependent claims describe other innovativecharacteristics of the invention.

[0015] Before describing the invention, it is appropriate to make someprior considerations.

[0016] One purpose of the invention is to achieve a device to obtain acontrolled bending, both positive and negative, of the rolling rolls,and in particular of the working rolls, in a rolling stand, which willbe effective and at the same time of limited size.

[0017] Another purpose of the invention is to achieve a device to bendthe rolling rolls which is mechanically simple and allows to obtain widebending, both static and dynamic and irrespective of whether it isnegative or positive, and thus to amplify significantly and decisivelythe field of regulation of the crown and the planarity of the product.

[0018] In accordance with said purposes, the device according to theinvention uses a configuration in which the bending actuators aredouble-effect type (FIG. 1b). Hence the space needed for theinstallation of the actuators is limited compared with the conventionalsolution according to the state of the art (FIG. 1a). The space occupiedis thus reduced and at the same time the capacity to perform positiveand negative bending is maintained.

[0019] In a rolling stand in which, for reasons of space, it isnecessary to adopt a configuration like that shown in FIG. 1b, withdouble-effect hydraulic jacks and with a hammer head (to attach to thechock), the situation is more complicated. It becomes difficult tocontrol bending around zero unless a solution is adopted with sixhydraulic jacks for each chock, but still with a particular managementof the bending forces of each hydraulic jack.

[0020] In substance it is necessary: (a) to prevent the hammer headhydraulic cylinder from working in a zone where friction and play renderinsecure the value of the force F actually transmitted by the jacks tothe chock; (b) to keep the actual total bending force (FTE) aligned onthe axis of the bearing of the working roll.

[0021] For point (a) it is necessary to manage the pressures in the twochambers of the hydraulic jack as indicated in FIGS. 4, 5a and 5 b. Thehydraulic jack can apply either a negative or positive force; Nindicates a hydraulic jack A when it applies a negative force, whereas Pindicates a hydraulic jack B when it applies a positive force.

[0022] In a configuration with four jacks for each chock, when jack B(FIGS. 4, 5a and 5 b) approaches the area of indetermination AI, it ismanaged with a negative bending force F− which is greater than needed,whereas, simultaneously, jack A generates a greater positive bendingforce F+ such as to balance the total result. In this way the passageinto the area of indetermination AI is achieved with the “plays” havingbeen recovered.

[0023] To respect the above condition (b), six hydraulic jacks can beused for each chock GWR, as shown in FIGS. 6 and 7. In this way notorques are generated in the bearing of the working roll WR.

[0024] With six jacks A the area of indetermination AI is managed asshown in FIG. 8 and the forces in play, for every single point F_(R),are those shown in FIG. 9.

[0025] It is also possible to adopt a solution with four jacks A foreach chock GWR. In this case the jacks A are managed differently betweenthe inlet side of the rolling stand and the outlet side thereof, asshown in FIGS. 10, 11 and 12, so that the force occurring on the bearingof the working roll WR is still aligned with the intersection betweenthe central axis C_(L) of the bearing and the rotation axis Y of theworking roll.

[0026] Therefore, the device according to the invention comprises twoseries of actuators for each chock associated with the rolls to be bent,each series being arranged on opposite sides of the corresponding chockwith respect to the axis of rotation of the roll to be bent.

[0027] The actuators are double-effect actuators and are housed in twodrawing sectors associated with the corresponding housing of the rollingstand.

[0028] Each actuator comprises a cylindrical rod provided with a hammerhead at one end thereof. The cylindrical rod is axially moved by commandmeans of a fluid-dynamic type.

[0029] The hammer heads of the two rods of each pair of actuators arehoused, advantageously with play, in the same longitudinal throughgroove made on one side of the chock. The two grooves of the same chockare parallel, so as to make it easy to remove the corresponding roll.

[0030] The travel of the cylindrical rods is sufficient both to bend theroll in both directions and also to recover the play between the hammerheads and the corresponding groove.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] These and other characteristics of the invention will becomeclear from the following description of a preferred form of embodiment,given as a non-restrictive example with reference to the attacheddrawings wherein:

[0032]FIG. 1a is a schematic view of a device to bend the rolls in arolling stand, according to the state of the art;

[0033]FIG. 1b is a schematic view of a device to bend the rolls in arolling stand, according to the invention;

[0034]FIGS. 2 and 3 represent diagrams able to show the behaviour of theforces in play in conventional devices;

[0035] FIGS. 4-12 represent diagrams able to show the behaviour of theforces in play in the device according to the invention, withdouble-effect bending actuators;

[0036]FIG. 13 is a schematic front view of a device as in FIG. 10;

[0037]FIG. 14 is a part section along the line from A to A of FIG. 13.

[0038] To be more exact, FIGS. 5a, 5 b, 7, 13 and 14 show the positionof the hydraulic jacks when working with bending in the area ofindetermination AI.

DETAILED DESCRIPTION OF A PREFERENTIAL EMBODIMENT

[0039] With reference to FIGS. 13 and 14, a device 10 according to theinvention is able to bend a roll 11, for example the working roll WR, ina rolling stand of a conventional type, with a pair of chocks 12 (onlyone of which is shown in the drawings) in which the ends of the roll 11are assembled able to rotate.

[0040] The device 10 comprises, for each chock 12, a series of actuators13 of the double-effect type, each of which comprises a cylindrical rod14. In the example shown there are two actuators 13 for each lateralside of each chock 12.

[0041] Each series of actuators 13 is housed in a corresponding block 15associated with the housing of the rolling stand. To be more exact, theblock 15 is of the type fixed to the housing of the rolling stand, ifthe working roll WR is not subjected to axial shifting, or movable withrespect to the housing, together with the corresponding working roll WRif the latter is able to shift axially.

[0042] Each rod 14 is connected with command means 17 of a conventionaltype, for example of the fluid-dynamic type and is provided, at one endopposite the command means 17, with a hammer head 18 which is housedwith play in a through groove 19, made on the lateral sides of eachchock 12.

[0043] The two grooves 19 are arranged on opposite sides with respect tothe axis of rotation Y of the roll 11, they are substantially T-shapedin cross section and they are parallel so as to make it possible toremove the roll 11.

[0044] Each hammer head 18 of the actuators 13 is able to cooperate bothwith the upper surface and also with the lower surface of thecorresponding groove 19. Moreover, the travel of the cylindrical rods 14is wide enough both to bend the roll 11, either negatively orpositively, and also to recover the play between the hammer heads 18 andthe groove 19.

[0045] The actuators 13 can be commanded either individually or inhomogeneous series, in one direction or the other, by the command means17, to obtain wide bends of the roll 11, both in the static and dynamicstep.

[0046] It is obvious however that modifications or additions can be madeto the device to bend the rolls in a rolling stand as describedheretofore, without departing from the spirit and scope of theinvention.

[0047] It is also obvious that, although the invention has beendescribed with reference to specific examples, a skilled person shallcertainly be able to achieve many other equivalent variants, all ofwhich shall come within the field and scope of this invention.

1- Device to bend the rolls in a rolling stand, wherein each roll to bebent (11) is rotatably mounted in two corresponding chocks (12)associated with command actuators (13) of double-effect type, whereinfor each of said chocks (12) two series of at least two of saiddouble-effect actuators (13) are provided, for a total of at least fouractuators (13) for each chock (12), wherein each one of said actuators(13) comprises a cylindrical rod (14) able to move axially under thecontrol of command means (17) of the fluid-dynamic type, characterizedin that each of said series of actuators (13) is disposed on oppositesides of the corresponding chock (12) with respect to the axis ofrotation (Y) of the roll (11) to be bent, and in that each of saidcylindrical rods (14) is provided with a hammer head (18) at one endopposite said command means (17). 2- Device as in claim 1, characterizedin that said hammer heads (18) of the cylindrical rods (14) of eachseries of actuators (13) are housed in a same longitudinal groove (19)made on the lateral sides of said chock (12) and shaped so as to receivesaid hammer heads (18) with play. 3- Device as in claim 2, characterizedin that each of said grooves (19) has a cross section substantiallyshaped like a T. 4- Device as in claim 2 or 3, characterized in that thetwo grooves (19) of the same chock (12) are through and parallel, so asto make it possible to easily remove the corresponding roll (11). 5-Device as in claim 2, 3 or 4, characterized in that each of said hammerheads (18) is able to cooperate both with the upper surface and alsowith the lower surface of the corresponding groove (19), the axialtravel of each of said cylindrical rods (14) being sufficient both tobend the roll (11) in both directions, and also to recover the playbetween the hammer heads (18) and the corresponding groove (19) and alsoto recover the variations in diameter of the rolls of the rolling standdue to the wear on the rolls themselves. 6- Method to bend the rolls ina rolling stand, wherein each roll to be bent (11) is mounted rotatablein two corresponding chocks (12) associated with command actuators (13)of double-effect type, characterized in that said command actuators (13)comprises hydraulic jacks with hammer heads, to attach to thecorresponding chock (12), and in that the bending around zero iscontrolled by using four or six of said hydraulic jacks for each chock(12). 7- Method as in claim 6, characterized in that steps are providedto obtain the following conditions: a) to prevent the hammer headhydraulic cylinder of each jack from working in an area ofindetermination (AI) where friction and play make unsure the value ofthe force (F) actually transmitted by said command actuator (13) to thechock (12); and b) to maintain the actual total bending force (FTE)aligned on the axis of the bearing of the roll to be bent (11). 8-Method as in claim 7, characterized in that said condition a) isobtained by acting on the pressures in each of the two chambers of thehydraulic jack (A, B) to apply both a negative and positive force. 9-Method as in claim 8, characterized in that in a configuration with fourjacks for each chock (12) a first jack (B), as it approaches said areaof indetermination (AI), is managed with a greater than necessarynegative bending force (F−), while, at the same time, a second jack (A)generates a greater positive bending force (F+), such as to balance thetotal result, so that the passage into the area of indetermination (AI)is performed with the play having been recovered. 10- Method as in claim7, characterized in that said condition b) is obtained by using sixhydraulic jacks (A, B) for each chock (12), so that no torque isgenerated in the bearing of the roll to be bent (11). 11- Method as inclaim 7, characterized in that said condition b) is obtained by usingfour jacks (A) for each chock (12), the management of said jacks (A)being different between the inlet side of the rolling stand and theoutlet side thereof, so that the resultant force on the bearing of theroll to be bent (11) is still aligned with the intersection between thecentral axis (C_(L)) of the bearing and the axis of rotation (Y) of saidroll to be bent (11).